Abstract

New simulation technique called the "system modal approximation" method for fluid transients in compound fluid-line systems is developed and presented. Unlike existing approaches based on the modal approximation of the input/output causality relationship of individual line element, this new method is based on the modal approximation of the frequency transfer function itself of the output (wanted variable) to the input (source) considering the dynamic characteristics of total system. This simulation technique also has the feature that only the numerical data of the frequency response of transfer matrix parameters of individual line element, which may be obtained from either theoretical model or experimental measurements, is needed and that the wanted output variable alone can be calculated selectively in the time domain by a simple algebraic expression in the form of recurrence formula. For complex fluid-line systems, the advantages of this technique over other existing modal approximation-based methods in accuracy, applicability, flexibility, computation time, etc. are discussed with experimental comparisons.

Keywords: fluid transients, water hammer, modal approximation, compound fluid-line system